The ability to effectively manage cross-functional working relationships (CFRs) during innovation is a key success factor in developing successful new products. However, empirical evidence suggests that CFRs during new product development are often problematic, resulting in extremely poor relations between managers, and the development of unsuccessful new products. This paper adds to our existing knowledge on the Marketing/R&D CFR by examining the effects of structural factors, communication behaviours, and interpersonal trust on the dependent variable perceived relationship effectiveness. Our findings reveal that trust has potent positive, direct effects on this CFR. Further, bidirectional communication and quality of communication also have strong effects on relationship effectiveness, as well as strong indirect effects via the building of interpersonal trust. In addition, we find that the structural variables formalisation and centralisation also influence communication behaviours on NPD projects.